1. Field of the Invention
The present invention relates to a method for simultaneously cutting off a multiplicity of wafers from a hard, brittle workpiece. The invention also relates to a device which is suitable for carrying out the method.
2. The Prior Art
The invention is useful in particular for the production of semiconductor wafers. For such applications, wire saws which are able to cut off a multiplicity of wafers from a workpiece in a single operation are increasingly being used. U.S. Pat. No. 5,771,876 describes the operating principle of a wire saw which is suitable for producing semiconductor wafers. The workpiece is guided through the wire web of the wire saw by a feed movement and, when it penetrates through the wire web, is divided into wafers. Wire saws which operate with a slurry are known, as well as other wire saws in which abrasive grains are fixedly bonded to the sawing wire. When cutting off semiconductor wafers from a crystal, it is usual for the crystal to be fixed at a mounting beam. The sawing wire then cuts the crystal at the end of the method. The mounting beam is a supporting body which is adhesively bonded or cemented to the peripheral surface of the crystal. After they have been cut off, the semiconductor wafers formed remain fixed to the mounting beam in the manner of the teeth of a comb and can thus be removed from the wire saw. Later, the residual mounting beam is removed from the semiconductor wafers.
When working with this kind of wire saws, the sawing wire may leave marks and waves on the sides of the wafers, which is undesirable. This is because they require more material to be removed during subsequent processes and because they make it difficult to measure the thickness of the wafers, and also constitute deviations from the desired wafer shape. For this reason, they have to be removed, for example by grinding, resulting in the loss of additional material.
JP-08-85053 A describes a method in which the workpiece is cemented to a mounting beam and, when the wafers are being cut off, carries out a pivoting movement, so that the sawing wire leaves a curved base in the sawing gap when penetrating into the workpiece.